Development of small-scale heating and sub-shock impact experiments for novel explosives*

At the novel design stage, explosive sensitivity is characterized by a suite of empirical methods, with the drop-weight impact test being one of the most common. Though the drop-weight test allows for the rapid and cost-effective characterization of explosive safety, reactions are identified by simple diagnostics such as sound level thresholds or gas production, which can obscure the complex initiation phenomena that are occurring. An impact generates heat through a range of compaction, flow, and dissipation mechanisms, which can lead to chemical decomposition, depending on the reaction rates of each explosive. In order to deconvolute the various contributions to the sub-shock ignition and propagation of explosive reactions, we will discuss the development, modeling, and early results for two new high-throughput tests designed for small amounts of explosives. The High Explosives Initiation Time (HEIT) test utilizes a 250 Joule pulsed power system to rapidly deliver electrical current to a small diameter needle filled with explosive, resulting in rapid and tunable heat delivery. Time-to-explosion data versus input temperature allow for Arrhenius kinetics information to be obtained and used in predictive modeling. Once an intrinsic sensitivity to temperature is established, we utilize plastic and viscous flow hydrocode modeling to predict how specific explosive samples will dissipate heat during rapid, sub-shock compression. These modeling results integrate with a second test, the Viscoplastic flow Ignition and Propagation Imaging of Reactions (VIPIR): a high-throughput, tunable drop tower with high-speed visible imaging. The history of previous rapid heating and drop tower experiments will be discussed in the context of these initial results.